This invention relates to electrically conductive brushes of a dynamoelectric machine and more particularly to apparatus which supports and manipulates brushes near a collector ring of a dynamoelectric machine.
As the power ratings of dynamoelectric machines have increased substantially in recent years, proper management of the large quantities of heat generated in current-carrying conductors of the machines has presented considerable challenge. The problem of avoiding overheating is particularly critical as the very large size of some components and the attendant difficulty of constructing and shipping certain units had made it desirable that increased ratings be achieved without further increases in size of certain components of the machine.
One part of the machine where increased current capacity is sought is the collector assembly, where higher ratings are desired without attendant increases in length or diameter of the dynamoelectric machine rotor. In this area, brushes of electrically conductive material such as graphite are typically used to transfer current from stationary portions of the machine to the rotating collector ring to furnish magnetizing power to the rotor field winding. Excess heat in this region can raise brush temperatures to high levels, causing rapid wearing of the brushes and necessitating their frequent replacement, and may also damage the collector ring.
Several devices to mount brushes in a dynamoelectric machine are shown in the prior art, including those described in the following patents assigned to the assignee of the present invention: U.S. Pat. Nos. 3,387,155 to Krulls; 3,432,708 to Bissett; 3,710,478 to Krulls et al; and 3,864,803 to Ohmstedt et al. Other brush assemblies are shown in U.S. Pat. Nos. 3,628,051 to Chigirinsky ulitsa Kuibysheva et al; 3,968,391 to Blank, and 3,983,432 to Rankin. Each of the patents cited above discloses apparatus permitting removal of brushes from the collector ring or rotating component of a dynamoelectric machine without shutdown of the machine. Also common to the disclosures of each of these patents is a box-like structure which contains and supports the brush to permit it to ride stably on the collector ring.
While these prior art devices allow a reduction in the labor involved in replacing worn brushes and avoidance of losses of power and time associated with stopping and re-starting the rotor of the machine, in certain applications the transfer of heat away from the brushes is impeded by the box-like structure these devices provide around the brush, which acts to shield a large portion of the brush from the surrounding gas, usually air. Although some machines, such as the turbine-generator whose excitation system is described in the paper "Experience With Alterrex Excitation For Large Turbine-Generators" by J. S. Bishop et al, presented in September 1974 at a Joint Power Conference of the Institute of Electrical and Electronics Engineers and American Society of Mechanical Engineers, incorporate fans to circulate air near the brushes and collector rings, such arrangements may be less efficient than desired, particularly as ratings are increased, since the fans must overcome the shielding effect of the brush boxes. As a result, excess power may be consumed in pumping air, or the brushes may operate at high temperatures and wear rapidly. Frequent inspection and replacement of the more than one hundred brushes of a typical large dynamoelectric machine can represent a significant maintenance expense.
Accordingly, it is an object of this invention to provide improved apparatus for supporting and manipulating an electrically conductive brush near a rotor of a dynamoelectric machine such that substantially all of the side surface area of the brush is exposed for unimpeded heat transfer away from the brush.
Another object of the invention is to provide brushholder apparatus wherein a brush is internally supported to improve heat transfer from brush surfaces and decrease brush wear.
A further object of this invention is to provide brushholder apparatus which includes a retainer to properly direct cooling gas near the brush and also includes means to permit safe removal and replacement of worn brushes without requiring shutdown of the dynamoelectric machine.